<!DOCTYPE html>
<html lang="en">

  <head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>邮箱显示案例</title>
  </head>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    .content {
      background-color: pink;
      width: 100px;
      text-align: center;
      margin: 0 auto;
      cursor: pointer;
    }

    .content a {
      text-decoration: none;
      display: inline-block;
    }

    .content ul {
      list-style-type: none;
      display: none;
    }

    .content ul li:hover {
      background-color: red;
    }

    .content:hover ul {
      display: block;
    }
  </style>

  <body>
    <div class="content">
      <a href="">邮箱</a>
      <ul>
        <li>163邮箱</li>
        <li>139邮箱</li>
        <li>QQ邮箱</li>
      </ul>
    </div>
  </body>

</html>